1. Field of the Invention
The present invention relates to a deceleration control system in a vehicle such as a motorcycle, a vehicle including the deceleration control system, and a deceleration control method of the vehicle.
2. Description of the Related Art
Japanese Utility Model Application Publication No. Hei. 6-43235 discloses a conventional deceleration system in a vehicle. This deceleration system determines whether or not deceleration (engine braking) resulting from a back torque transmitted from a drive wheel toward a driving power source is rapid, based on a vehicle speed and a shifted gear position, when a throttle valve in an engine is fully closed. If the deceleration is rapid, an air control valve provided auxiliarily with the throttle valve is opened, so that air is supplied to the engine.
In the conventional deceleration system, the air control valve operates in a uniformly fixed manner after it is determined that the deceleration is rapid, and the degree to which deceleration is mitigated is constant. The magnitude of an engine braking force changes according to a driving state of a vehicle. Therefore, the degree to which deceleration is mitigated is insufficient or in excess if the air control valve operates in a fixed manner.